Transparent substrates with a transparent conductive film that each includes a transparent substrate, such as glass, and a transparent conductive film formed thereon are used for photoelectric conversion elements, optical sensors, image displays, light emitting devices, etc., with a functional thin film further being formed on the transparent conductive film. Examples of the image displays include liquid crystal displays, organic EL displays, and plasma displays. Examples of the light emitting devices include field emission displays (FEDs), light emitting diodes, and solid state lasers.
The transparent substrates with a transparent conductive film also are used as, for instance, window glass for buildings, window glass of refrigerators for stores, and document glass of copying machines, specifically Low-E (Low-Emissivity) glass, electromagnetic wave shielding glass, and defogging glass.
A photoelectric conversion element is an energy conversion element that converts optical energy into electric energy or vice versa. A solar cell converts optical energy into electric energy. A solar cell with a silicon semiconductor thin film includes a configuration in which a silicon semiconductor film (a photoelectric conversion layer) with a photoelectric conversion function and a back electrode film are formed sequentially on the transparent conductive film of a transparent substrate with a transparent conductive film.
Sunlight that has entered the transparent substrate with a transparent conductive film from the transparent substrate side passes through the transparent conductive film to reach the photoelectric conversion layer. Electric energy produced in the photoelectric conversion layer is taken out through the transparent conductive film and the back electrode film.
In order to improve the sunlight conversion efficiency, it is desirable to increase the amount of light that reaches the photoelectric conversion layer. An effect of improving the conversion efficiency also is provided when concavities and convexities are formed at the surface of the transparent conductive film to confine light in the photoelectric conversion layer. Many experiments and proposals have been made with respect to the techniques for forming concavities and convexities at the surface of the transparent conductive film.
JP61(1986)-288314A and JP61(1986)-288473A each disclose a technique for forming concavities and convexities by chemically etching the surface of a transparent conductive film. This technique, however, results in lower productivity since it is necessary to employ additional processes such as an etching process, a process for removing an etchant by water washing, a drying process to be carried out after the water washing, etc.
WO03/36657 discloses a technique for forming a first undercoating layer that is tin oxide formed in a discontinuous dome shape, a second undercoating layer that is a continuous silicon oxide film, and a continuous tin oxide conductive film on a transparent substrate in this order. However, when this technique is used to form concavities and convexities with a height of at least 200 nm, unevenness in haze is caused that can be observed visually. The substrate with a transparent conductive film formed using a dome-shaped undercoating still is susceptible to improvement.
JP5(1993)-67797A discloses a transparent conductive substrate for solar cells that includes a crystalline tin oxide film formed of two layers on a glass sheet. In this substrate, tin oxide of the lower layer is oriented in a (110) plane while tin oxide of the upper layer is oriented in a (200) plane. FIG. 16 of JP5(1993)-67797A shows the relationship between the thickness of the lower layer and the haze ratio of the whole film. According to this figure, the haze ratio of the whole film is not higher than about 10%.